How to add group as reviewers in MR by non-group member?

We have onshore members has group, when offshore members try to add onshore group as reviewers in MR , they are not able to add the group.

For Eg:

  1. We have created TEST group in gitlab for project
  2. Members in TEST group are A,B,C(On shore members are part of group)
  3. When off shore members(not part of TEST group) are try to add TEST group as reviewer in MR request not able to add.